Sorry to have let you down for so long. Set theory was keeping me busy, and I wanted to come back to you with a decent answer. So there we go.

Best,S

1) Your claim: there is social and racial discrimination in our society and people suffer from it.

You give several reasons and question my objectivity on this issue:• "Racism/inequality/structural exclusion, in their many faces, are a fact, a reality."• "I had a colleague in school [who] was told by her advisor to pursue a two-year degree instead of a bachelor's degree because she was Hispanic and a woman"• M.Gladwell's article on The chosen in the New Yorker• "when you come across a book that doesn't support [this idea] you simply invoke lack of time as a reason for not reading it"

I am not denying in any way that racial and social discrimination exist and that people suffer from them. I don't know how it feels to belong to a minority in my country, and wish no one had to know (see also this book to understand why I didn't feel an urge to read The chosen). But the question I asked during our conversation in Luxembourg was different: do these discriminations really have a large influence on people's achievement in higher education (nowadays, in the US)?

2) My conjecture: at college level, cognitive aptitude is now more important than social origin to obtain a degree, and affirmative action has more than compensated the negative effects of racial discrimination.

This is based on NLSY data as compiled in The bell curve. Overall, there have been some – although comparatively few – critics about the source data and the way the authors did their computations. What they claim is that once students reach the point of entering college, social discrimination does not make a huge difference, and affirmative action even makes life easier for a black student than for a white or an asian student. Note that this does not contradict the existence of discriminations. Although in my view this result is not very difficult to accept, many people reply that it does not compare like with like. In their view, socially or racially discriminated people either don't go far enough to apply for college, and when they do, their IQ only reflects the negative impact of their condition. To support this view, there is the lieu commun that "people are created equal", so that in order to be found unequal later they must have endured a different treatment.

This was reflected in your comments:• In recife, the city where I lived in Brasil, there is a preparatory school where most rich kids attent to ensure success in the highly competitive college entrance exams• Suppose that both groups had to pass the same standarized test. In terms of mathematics, they would certainly outperform the rest of us as a group. Does this mean that they had all a higher IQ? That they had all greater learning potential? That they were more mathematically adept than us? No, it means its simply a difference in curriculum.

This debate naturally leads to the question: are people created equal? Incidentally, this is the reason for which I got interested in IQ and The bell curve in the first place. In economics, considering the fact that people have unequal levels of revenue, you have to wonder if they run different races ceteris paribus, or run the same race but simply have unequal aptitudes (it could also depend on luck for that matter). This is not to imply that life should only be seen as a competition, but the analogy has some merit. I hope this will answer a comment you made:• I sincerely hope you abandon this (in my opinion flawed) fascination with IQ and The bell curve.

3) My claim: there is solid evidence that some innate attributes reflected in the index called IQ play an important role in scholar and economic achievement

On IQ you wrote:• Does a 6 month old have the same IQ as a 6 year old? A 6 year old vs a 15 year old?• What does the variation in IQ really tell us about the person? [Can the IQ predict if a person is a hard worker? Disciplined or scatter brain? Musically gifted? A great novelist?] Can IQ really predict the level of productivity an individual will attain in the right environment?• Also, you might want to consider the discussion regarding standardized/IQ tests as cultural products or constructs.

These are good questions to test the validity of IQ, and the answer to both of them is roughly yes (except for those between brackets). From what I have read, IQ is quite stable along the life of a grown-up child and adult, and is a better predictor of professional peformance than most other tests. As for artistic creativity, discipline and so on, psychologists consider them to be separate personality traits. They all differ from IQ in a very important respect: they are much less heritable, in the order of 40% or less versus 60% or more for IQ. Finally, IQ is correlated with biological variables such as cranial volume and the speed of some nervous reaction in the brain.

So what exactly is IQ and how is it measured? Early in the 20th century, a psychologist named Spearman observed that scores in various tests were often correlated. Because they varied simultaneously, he thought that they could have a common factor which he named the g factor for general intelligence. The IQ test was then designed to extract the largest possible part of the variance of various other tests such as English, memory, math, SAT, etc. Because of numerous attacks against them, IQ tests have since evolved. Among the most recent versions, those based on Raven matrices are purely graphical, non-verbal and non-math, and well tested against cultural and social bias when taken under controlled conditions. In the Bell curve, the authors use scores from an armed forces test called AFTQ which is heavily loaded in g. From this perspective, it appears that many things that we considered to be largely determined by our social and cultural group, such as economic and educational achievement, are nowadays related more to IQ than to anything else.

This being said, we know very little about what might influence IQ apart from genes. This is a surprising statement, as we would have expected parenting and schooling to have a major influence. In fact, it seems that the non-genetic variance of IQ has little correlation with our family environment, and education programs such as head start or even more intensive programs seem to have almost no lasting effect on IQ. From what I have read, this remains an open question in modern psychology (see for instance this book). Of course, it is true in our countries only because the vast majority of children get a decent environment and education, and it does not preclude that a dramatic environment can permanently alter a child's development.

So, going back to our question about higher education, what if people actually do run the same race, but have different aptitudes either for genetic or unknown reasons? What should we do about it?

4) Your claim: it is both useless and morally wrong to compare human beings, most of all when this comparison is based on their belonging to a "racial" group

You wrote:• we keep on referring to "race" as if it were a real thing• I find it insidious, and downright dirty, to suggest, even if indirectly, that one racial group (in this case, black) might be intellectually inferior to others.• a few people in the past and present (you not being the first one) have tried to qualify these differences in order to introduce and enforce policy, from segregation all the way to genocide. We just need to be careful not to qualify these differences once we agreed that they are quantifiable...• Focusing on the supposed inferiority of a group rather than on correcting the strucutural factors that have led to or contributed to the "state of affairs" seems, therefore, to be self-serving and completely unproductive.• The worst part of the IQ line of thought is that people actually would like to base policy on some statistical studies involving IQ.

I agree with all these statements, most of all with your provision about the "black–inferior" thing: having a lower IQ should never be considered an "inferiority", regardless of skin color. Yet IQ differences do exist, and the confusion with "class" often arises as soon as we try to measure it or other things ( S.J.Gould's book is a good example). Maybe this is due to our tendancy to think in terms of "good" and "bad" or in terms of a vertical rather than horizontal scale.

So to the question asked above, "What should we do about IQ?", I answer "Nothing, just let it be". What I mean by that is that public policies should not be concerned with people's IQ. Also, they should not try to change IQ as they have sometimes been trying to, all the more since we don't even know how to do it. From my liberal perspective, each individual should be considered responsible for making what he/she wishes of his life with no external interference every time it is possible. Those who are physically or mentally unable need to be helped, but the rest of us can each try his own way. We will be sometimes lucky, sometimes not, but this is also part of the thrill!

To end on a lighter note, I will go back to the "taller men" theory, as you stated in one of your mails:• Well... I'm not sure if it's 'your' theory, but even if it were, it can be debunked just as well. Who says taller men get married earlier? And what does this mean in terms of procreating taller children? So my question is, why are these people getting taller and why are taller men so much more desirable that average but intellectually successful men?

As you can guess, I would be delighted to find some scholar supporting the idea. At first, I was sure I had read about this theory it somewhere. I remain convinced that someone must have come up with this idea before me, but I have found no evidence on Internet yet. So how could this work? Very simply: women prefer taller men (for no good reason, but as a state of facts), and the rest follows. The evidence to support this outrageous idea is given by the INSEE statistics, which show beyond doubt that in France taller men get married earlier, more often, and have more children. All of those contribute to the faster replication of their genes. I don't know if you will share my feeling, but this makes me absolutely hilarious and rather glad to be so brought back to my condition of "thinking animal".